A conventional automotive disk brake pad comprises a metal backing plate to which is attached a pad or block of a friction material. The mode of attachment varies according to circumstances. One method which is in wide use is based on previously prepared friction material pads. The raw materials for the pad including resin binders, are compounded, usually in powder or dough form, and thereafter compacted in a molding tool, under heat and pressure until the pad binder system has fully cured to form a rigid block. This block is then surface ground, to remove flash and to flatten its opposed front and back faces. It is then drilled and countersunk prior to rivetting onto a previously drilled backplate.
Another method which is in fairly wide use is to prepare a disk brake pad as a partially compacted and partially uncured preform. In such a preform, the resin binders are partially cured. A metal backing plate with several apertures in it is prepared, first by cleaning and then by coating with an adhesive, the latter being normally subjected to a heat treatment effective to dry the adhesive and cause it to partially cure, (commonly referred to as "B-stage" curing.) The pad preform is placed onto the adhesive coating and compacted to its final size and density through the application of heat and pressure. During this operation, some of the preform material is extruded into the apertures in the backplate, thereby keying the pad and plate together. Also, the adhesive is caused to set, bonding the shaped preform firmly to the backplate, without the need for rivets. Such assemblies are referred to as integrally molded.
A problem with conventionally manufactured disk brake pads is noise generated by the braking action. Several proposals for alleviating the problem are known. For example, one can fit a shim between the brake pad and the associated caliper. The shim is in the form of a thin metal sheet or layer coated on at least one face with a rubber composition. The latter acts as a damping element for the purpose of sound transmission/generation. However, the manufacture of suitable shims is an extra production process; their inclusion into the brake assembly is generally inconvenient. Also, it is possible for the shims to be omitted inadvertently during servicing operations.